Hydroformylation process with recycle of active rhodium catalyst

ABSTRACT

The present invention relates to a continuous hydroformylation process for the production of an aldehyde by hydroformylation of an olefin which comprises: providing a hydroformylation zone containing a charge of a liquid reaction medium having dissolved therein a rhodium hydroformylation catalyst comprising rhodium in combination with carbon monoxide and a ligand; supplying the olefin to the hydroformylation zone; maintaining temperature and pressure conditions in the hydroformylation zone conducive to hydroformylation of the olefin; recovering from the liquid hydroformylation medium a hydroformylation product comprising aldehyde; recovering from the hydroformylation zone a stream comprising the rhodium catalyst; contacting at least a portion of the stream with a solid acidic absorbent under process conditions which allow at least some of the rhodium to become bound to the absorbent; subjecting the rhodium bound to the absorbent, under process conditions which allow desorption of the metal, to a fluid stripping medium comprising hydrogen and solvent; recovering the rhodium hydride catalyst; and recycling the rhodium hydride catalyst to the hydroformylation zone.

FIELD OF THE INVENTION

The present invention relates to an improved hydroformylation process.In particular, it relates to a process for the hydroformylation ofolefins to give aldehydes. Most particularly, it relates to a processfor the hydroformylation of C₂ to C₂₀ olefins or higher in which processconditions may be used which have not been possible heretofore.

BACKGROUND OF THE INVENTION

Hydroformylation is a well known reaction in which an olefin, usually aterminal olefin, is reacted under suitable temperature and pressureconditions with hydrogen and carbon monoxide in the presence of ahydroformylation catalyst to give an aldehyde, or a mixture ofaldehydes, having one more carbon atom than the starting olefin. Thus ahydroformylation reaction with propylene will yield a mixture of n- andiso-butyraldehydes, of which the straight chain n-isomer is usually themore commercially desirable material. The hydrogen and carbon monoxidewill generally be supplied to the hydroformylation reactor as synthesisgas.

Examples of hydroformylation processes can be found in U.S. Pat. Nos.4,482,749, 4,496,768 and 4,496,769 which are incorporated herein byreference.

The catalysts first used in hydroformylation reactions werecobalt-containing catalysts, such as cobalt octacarbonyl. However, thepresence of these catalysts meant that the reactor had to be operated atexceptionally high pressures, e.g. several hundred bars, in order tomaintain the catalysts in their active form.

Rhodium complex catalysts are now conventionally used in thehydroformylation of both internal olefins and alpha-olefins, that is tosay compounds containing the group —CH═CH₂, —CH═CH—, >C═C<, >C═CH—,—CH═C< or >C═C₂H. One advantage of these catalysts is that loweroperating pressures, e.g. to about 20 kg/cm² absolute (19.6 bar) orless, may be used than was usable with the cobalt catalysts. A furtheradvantage noted for the rhodium catalysts was that they are capable ofyielding high n-/iso-aldehyde product ratios from alpha-olefins; in manycases n-/iso-aldehyde molar ratios of 10:1 and higher can be achieved.

Further, since the rhodium catalyst is non-volatile, product recoverywas greatly simplified. A fuller description of the process can be foundin the article “Low-pressure OXO process yields a better product mix”,Chemical Engineering, Dec. 5, 1977. Also relevant to this process areU.S. Pat. No. 3,527,809, GB-A-1338237 and GB-A-1582010 which areincorporated herein by reference.

The rhodium catalyst generally adopted in commercial practice comprisesrhodium in complex combination with carbon monoxide and with anorgano-phosphorous ligand, for example triphenylphosphine. Although thenature of the catalytic species is not entirely clear, it has beenpostulated that where the ligand is triphenylphosphine it isHRh(CO)(PPh₃)₃ (see, for example, page 792 of “Advanced InorganicChemistry” (Third Edition) by F. Albert Cotton and Geoffrey Wilkinson,published by Interscience Publishers).

The reaction solution for the hydroformylation reaction will generallycontain excess ligand.

U.S. Pat. No. 3,527,809, which is incorporated herein by reference,proposes the use of other ligands, including phosphites, such astriphenylphosphite.

Whilst the use of rhodium catalysts offers various advantages, it doessuffer from the disadvantage that it is very expensive. It is thereforedesirable to utilise this highly expensive metal in the mosteconomically effective way.

During operation of the reactor, the catalyst may become deactivated andtherefore needs to be removed from the reactor such that fresh activecatalyst can be added. The removed catalyst will generally be processedto recover the metal values.

The deactivated catalyst may have been thermally deactivated, i.e.clustered and/or chemically deactivated, i.e. poisoned or inhibited.

In some cases although the catalyst may be chemically active, thecatalyst solution includes such a high concentration of non-volatilematerial that it is of no further practical use.

Although the mechanism of deactivation in aryl phosphine ligandedsystems by the formation of clusters is not entirely clear, it isbelieved that rhodium clusters, having phosphido bridges may be formed,for example, by the loss of one or more phenyl groups from the arylphosphine molecule. The formation of clusters is generally increased asthe temperature is increased.

The chemical deactivation may be poisoning such as by sulphur compounds,chloride, cyanide and the like.

The chemical deactivation may also be inhibition of the catalyst.Inhibitors that may be found in, for example, propylene and butylenehydroformylation include acetylenes and acroleins.

Since the rhodium catalyst is generally used in low concentrationbecause of its high cost and activity, the effect of any poisons orinhibitors present is high. It is therefore usually necessary to reducethe presence of these poisons and inhibitors present in the feed to verylow levels.

Rhodium catalysed hydroformylation processes can be classified into twomain categories, namely those in which the aldehyde product is removedby liquid/liquid separation processes and those in which the product isremoved by a vapour path process.

In the processes in which the aldehyde product is removed by aliquid/liquid separation process, the aldehyde product is obtained asone liquid phase while the ligand and rhodium/ligand complex remains inanother phase and is returned to the reaction zone. This type of processhas the advantage of being independent of the volatility of the aldehydeproduct and the volatility of the relatively less volatile aldehydecondensation by-products. These processes do, however, have their owndisadvantages including interphase solubility/entrainment problems inwhich some of the rhodium may leave in the aldehyde product-containingphase, low selectivity to the desired aldehyde isomer and low reactionrate as a consequence of the low solubility of the reactants in anaqueous base reaction medium.

Where the aldehyde product is recovered from the catalyst by a vapourpath process this has conventionally been effected in one of two ways.

Where lower olefin feedstocks are used, a stream of synthesis gas andolefin is passed through the reactor solution, condensed and afterseparation of the liquid condensate the gas phase is returned to thereactor via a compressor. Suitable means is used to prevent the rhodiumsolution leaving the reactor by liquid droplet entrainment in the gasphase these include restricting the superficial velocity of the gasthrough the reactor to less than a specific value and passing thegas/vapour stream through a liquid droplet de-entrainment device beforeexiting the reactor. Addition of make-up streams of synthesis gas andolefin are required to maintain the system pressure and reaction rate asthe reactants are consumed. A purge stream of gas after the condensationstage is generally required to remove any inert gases accumulating inthe system and also to control the level of paraffins that either enterthe system with the olefin feed or are produced by olefin hydrogenationin the reactor. This type of process is generally known as a Gas RecycleProcess.

An important feature of the Gas Recycle Process is that to achievestable reactor conditions, every product of the reaction must leave thereaction system at it's rate of formation, thus the relatively lessvolatile materials (such as aldehyde condensation products) accumulatein the reactor solution to a relatively high concentration until therate of removal of products in the vapour phase equals the productionrate of each material. This can be achieved for long periods when thefeed olefin is ethylene or propylene but even with propylene there canbe a slow accumulation of aldehyde condensation tetramers and pentamerssuch that the reactor solution volume will slowly increase with time.

If progressively higher olefins such as butenes, pentenes, hexenes etc.are supplied to a gas recycle system the requirement for a higher gasrecycle rate means that the gas superficial velocity limit is exceededunless a reactor solution volume that is increasingly wide and shallowis used as the olefin molecular weight increases. Thus, whilst thisarrangement goes some way towards addressing the problems detailedabove, the arrangement suffers from new problems associated withgas/liquid mass transfer and reactor mechanical/economic design issues.

In an alternative solution to the problem associated with the use ofhigher olefins, the temperature of the reaction system is increased suchthat every component becomes more volatile. Again, whilst thisarrangement goes some way to solving the above problem, fresh problemsare noted. In this case, increased production of heavy aldehyde selfcondensation by-products and increased catalyst deactivation byincreased clustering rates occurs.

These considerations mean that the Gas Recycle Process is limited to thehydroformylation of ethylene and propylene with the hydroformylation ofbutenes and pentenes being marginal and very marginal casesrespectively.

These considerations led to the development of the so called “LiquidRecycle Process”. In this process a volume of solution is continuouslywithdrawn from the hydroformylation reaction zone or zones such that theliquid level in the or each zone is held constant. This withdrawn liquidis then subjected to a single or multistage evaporation operation wherethe temperature, pressure and residence times are selected to recoverthe products and by-products as well as to protect the catalystactivity. The concentrated catalyst solution is then returned to thehydroformylation reaction zone. Olefin and synthesis gas are supplied tothe or each hydroformylation reaction zone to maintain the desiredreaction rate and conditions.

The liquid recycle process has been shown to provide benefits even forthe hydroformylation of propylene where higher volumetric productivityand lower operating costs can be achieved, and is essential for theeconomic production of C₅ and higher aldehydes.

As olefins of increasing molecular weight are hydroformylated by theLiquid Recycle Process the removal of the heavy by-products byevaporation requires lower and lower pressures and/or higher evaporationtemperatures. Thus, despite the advantages noted for this process,eventually the accumulation of heavy by-products in the reactor solutionoccurs such that the reactor volume increases uncontrollably. Thisdisadvantage of the system is referred to as “heavies drowning”. Whereheavies drowning occurs, there has to be a purge of catalyst solution(containing ligand and active catalyst) to control this accumulation.

It has been suggested, for example in U.S. Pat. No. 5,053,551, that theaddition of inert diluents can delay heavies accumulation to defer theheavies drowning effect and confer a longer useful catalyst life. Whilstthe system goes some way to addressing the problem, it cannot preventeventual heavies drowning from occurring.

Thus during the operation of a liquid recycle hydroformylation plant thereaction and product recovery conditions are in a state of continuouschange due to the changes in solution composition and catalyticactivity. The accumulation of essentially non volatile aldehydecondensation products requires that the pressure and/or temperature ofthe product evaporator needs progressive adjustment. The accumulation ofinhibitors and poisons in the reactor solution also requires theprogressive adjustment of reaction conditions to maintain the conversionand selectivity of the system. High temperature evaporation and poisonsin the olefin feed can also result in the loss of catalytically activerhodium by poisoning and/or the formation of rhodium clusters requiringthe continuous or periodic removal of a part of the catalyst recyclestream and its replacement by fresh catalyst and ligand.

Thus, it will be understood that whichever hydroformylation method isselected, the economic need to run the plant for maximum production ofproduct must be balanced with the need to conserve the life of theexpensive catalyst. It is therefore desirable to adopt catalystmanagement systems which maximise productivity whilst minimising thedamage to the catalyst.

One catalyst management system which may be adopted comprises charging afirst charge of catalyst to the plant. As the productivity of the plantbegins to decline it is necessary to adapt the utilities and separationunits of the plant to the reduced flow of aldehyde and the reducedconsumption of synthesis gas. Care is taken to ensure that thetemperature does not increase since any such increase will result in anaccelerated decline in the catalyst activity and increased formation ofthe heavies. When product flow falls to a level that is unacceptable,the plant operator may choose to raise the temperature with theattendant problems or add additional catalyst.

Although increasing temperature does have the drawbacks detailed aboveit does not incur the capital expenditure of catalyst purchase and maytherefore be the preferred initial approach. Any step change in thetemperature will require a corresponding step change in the operation ofthe utilities and separation units.

After any increase in temperature the productivity will continue todecline but at an increased rate. Further increases in temperature maybe carried out until a decision is made that any further increase willresult in an unacceptable rate of catalyst deactivation. At this pointfurther catalyst may be added to the reactor. However, increasing thecatalyst concentration will also increase the rate of thermaldeactivation and the consequential loss of activity. Thus there is anupper practical limit on the amount of rhodium which may be added to thereactor. Eventually it will be necessary to shut down the plant.

One alternative catalyst management system involves taking a continuouspurge of the reactor solution which can then be reprocessed to recoverthe catalyst and remove the heavies. In practice, economics require thatthe catalyst be reprocessed in large batches and results in significantloss of rhodium metal. This results in high capital expenditure for theplant owners.

Where triphenylphosphine is used as ligand, it may react with the olefinto produce the corresponding alkyldiphenylphosphine. Since thealkyldiphenylphosphines are stronger complexing agents than thetriphenylphosphine, a catalyst solution of lower activity andselectivity to the linear product is obtained.

These mechanisms of catalyst degradation become progressively moreonerous as the molecular weight of the olefin increases, requiringprogressively higher catalyst purge rates.

Conventionally, the operators of the gas or liquid recycle plant havehad to collect the active and/or inactive catalyst by shutting down thereactor, removing some or all of the catalyst solution and concentratingit to partially separate it from the other components present.Additionally, or alternatively, partially deactivated or heavies drownedcatalyst may be continuously collected from reactor streams. By reactorstream we mean any stream which is obtained from any point in a processand which will contain rhodium metal catalyst. In the case of the liquidrecycle process, the stream will usually be the catalyst recycle streamafter evaporation of the hydroformylation products.

The conventional liquid recycle process must therefore be subjected to acontinuous or episodic regime of adjustment in process conditionsthroughout the operating period and this is particularly marked when thehigher molecular weight olefins are used as feedstock.

Since the rhodium is generally only present at low concentration, it canbe particularly difficult and costly to recover the rhodium from thevery dilute solutions.

The rhodium organic solution has conventionally been concentrated by avariety of means before being shipped off-site for recovery. This meansthat if the operation of the plant is not to be shut down for aprolonged period, the operator must purchase more of the very expensivecatalyst to operate the plant than he actually requires at any one time.

There are also environmental issues associated with the recovery of thecatalyst where phosphorous ligands are present.

A variety of means of recovering the rhodium from solution has beensuggested including precipitation followed by extraction or filtrationand extraction from the organic mixtures using, for example, aminesolutions, acetic acid, or organophosphines.

Ion-exchange methods have also been suggested, for example in U.S. Pat.No. 3,755,393 which describes passing a hydroformylation mixture througha basic ion-exchange resin to recover rhodium. A similar process isdescribed in U.S. Pat. No. 4,388,279 in which Group VIII metals arerecovered from organic solution using either a solid absorbent such ascalcium sulfate, an anionic ion-exchange resin or molecular sieves.

An alternative arrangement is described in U.S. Pat. No. 5,208,194 inwhich a process is described for removing Group VIII metals from organicsolutions which comprises contacting the organic solution with an acidicion-exchange resin containing sulfonic acid groups. The treated solutionis then separated from the ion-exchange resin and the metal values arerecovered from the resin by any suitable means. One means that issuggested is that the resin should be burnt off in an ashing processwhich leaves the metal in a form suitable for recovery.

These prior art processes, whilst being suitable for separating themetal from the stream in which it was removed from the reaction, sufferfrom the disadvantage that the operator of the reactor must send therecovered metal concentrate off-site to be converted into an activeform. Further, where the stream removed from the reactor includes activecatalyst, the separation procedure will either leave it in a form inwhich it cannot be returned to the reactor or will cause it to bedeactivated such that it is no longer suitable for use in the reactorand removal off-site for regeneration is required.

In U.S. Pat. No. 5,773,665, a process is suggested which enables activecatalyst contained in a stream removed from a hydroformylation processto be separated from the inactive catalyst and the active catalystfollowing treatment, to be returned to the hydroformylation reactor. Inthe process a portion of the recycle stream from the hydroformylationreaction is passed through an ion exchange resin column to removeimpurities and active rhodium and the thus purified recycled stream,which may contain inactive catalyst, is returned to the hydroformylationreactor.

The impurities, which may include aryl phosphine oxide, alkyl phosphineoxide, mixed phosphine oxide and high molecular weight organiccompounds, are removed from the resin by washing with, for example, anorganic solvent. The effluent from this wash is removed as a wastestream. The active catalyst remains bound to the resin during thiswashing process.

The resin is then treated with a catalyst removal solvent such asisopropanol/HCl to produce a stream containing “active” rhodium catalystfor eventual recycling to the hydroformylation reactor. Whilst thecatalyst has not been deactivated by thermal or chemical means and istherefore referred to as “active” it is not in a form in which it willactually act as a catalyst in the reactor. Thus, before the catalyst canbe recycled it must first be removed from the resin using a strong acidreagent and then converted to the hydridocarbonyl by treatment withhydrogen and carbon monoxide in the presence of an acid scavenger and aligand to make it a truly active catalyst.

In an optional arrangement, the inactive rhodium catalyst, i.e. theclustered catalyst, which passed through the ion-exchange resin withoutbeing absorbed and which is contained in the purified recycle stream maybe reactivated by conventional technology such as by wiped filmevaporation followed by oxidation and subsequent reduction before beingreturned to the reactor. Thus this inactive catalyst is not treated bythe ion-exchange resin.

Whilst this process goes some way to improving the conventionalhydroformylation process by recycling some of the rhodium, in that itsuggests a means of separating the active catalyst on site, it suffersfrom various disadvantages and drawbacks in particular thosedisadvantages associated with the need to treat the “active” catalystafter it has been removed from the ion-exchange resin and before it canbe returned to the reactor. Indeed it is the ion-exchange treatmentwhich means that the catalyst is no longer suitable for use in thereactor. Although in a preferred embodiment, U.S. Pat. No. 5,773,665does suggest that the thermally deactivated catalyst may be regeneratedbefore return to the reactor, the overall plant described therein isexpensive to construct and operate because of the number of separationand treatment steps required to achieve full recycle. The problem isparticularly exacerbated as some of the steps are carried out in thepresence of corrosive acid media A further drawback associated with thepresence of acid media is the costs associated with the consumption ofbase required to neutralise the acid.

There is therefore a desire to produce a process for the production, ona continuous basis, of aldehydes from olefins by hydroformylation usinga liquid recycle process under constant conditions chosen by the plantoperator for extended, preferably indefinite, periods of time whilstproviding maximum utilisation of the catalytic metal and ligand.

SUMMARY OF THE INVENTION

Thus according to the present invention there is provided a continuoushydroformylation process for the production of an aldehyde byhydroformylation of an olefin which comprises:

-   -   (a) providing a hydroformylation zone containing a charge of a        liquid reaction medium having dissolved therein a rhodium        hydroformylation catalyst comprising rhodium in combination with        carbon monoxide and a ligand;    -   (b) supplying the olefin to the hydroformylation zone;    -   (c) maintaining temperature and pressure conditions in the        hydroformylation zone conducive to hydroformylation of the        olefin;    -   (d) recovering from the liquid hydroformylation medium a        hydroformylation product comprising aldehyde;    -   (e) recovering from the hydroformylation zone a stream        comprising the rhodium catalyst;    -   (f) contacting at least a portion of the stream with a solid        acidic absorbent under process conditions which allow at least        some of the rhodium to become bound to the absorbent;    -   (g) subjecting the rhodium bound to the absorbent, under process        conditions which allow desorption of the metal, to a fluid        stripping medium comprising hydrogen and solvent;    -   (h) recovering the rhodium hydride catalyst; and    -   (i) recycling the rhodium hydride catalyst to the        hydroformylation zone

In a most preferred arrangement, the stream from step (e) is divided anda first part is recycled to the hydroformylation zone and the secondpart is subjected to steps (f) to (i). Any suitable amount of dividedstream may be passed to steps (f) to (i). However, the substantialbenefits of the present invention are achievable even if small amounts,such as amounts of the order of 1% or even less such as amounts of theorder of 0.01%, are subjected to steps (f) to (i).

It will be understood that the recycled rhodium hydride catalyst fromstep (i) will be utilised in the further hydroformylation reaction.

The stream recovered from the hydroformylation zone in step (e) may beany stream which is obtained from any point in the hydroformylationprocess and which will contain rhodium metal catalyst. In the case ofthe liquid recycle process, the stream will usually be the catalystrecycle stream after evaporation of the hydroformylation products.

The arrangement of the present invention enables substantial benefits tobe obtained. First, the recovery and recycling of the present inventionenables the plant operator to run the plant with less catalyst than hasbeen required heretofore. This is because it is not necessary to holdcatalyst in stock to replace catalyst which is shipped off-site forrecovery and regeneration.

The catalyst recovery arrangement of steps (f) to (i) are particularlyefficient in separating catalyst from heavies and therefore the systemallows for the heavies formation in the reactor or elsewhere in thesystem to be readily managed without having a deleterious effect on theoperation of the reactor. This is because the process of the presentinvention is particularly suitable for removing the rhodium hydridecatalyst from reactor streams containing molecules having a highmolecular weight and hence low volatility and which are thereforedifficult to separate from the catalyst by conventional means.

Examples of these heavies, which are generally high boiling by-products,include organic condensation products and will include cyclic trimersand higher cyclic moieties and linear and branched polymeric moietieswhich could also be present in the feed to the reactor.

Further, the presence in the system of the catalyst recycle allows forcontrol of the level of non-volatile inhibitors present in the reactorsystem and may facilitate long term operation at constant reaction andvaporiser temperatures.

Since the catalyst can be readily recovered and/or heavies readilyremoved, by the process of the present invention, the plant operator maychoose to operate the plant at conditions which have heretofore not beenpracticable because of catalyst deactivation and/or heavies formation.Thus, for example, higher temperatures in both reactor and vaporiser maybe usable which will enable an increased rate of production of thealdehyde.

Thus the present invention provides a hydroformylation process in whichcontinuous recycling of the rhodium catalyst allows for the overallproductivity to be maintained constant despite on-going deactivation ofthe catalyst and heavies formation. As this allows for the previouslyrequired step changes in productivity to be obviated, the ease ofoperation and the efficiency of the reaction is enhanced. The processmay also allow feedstocks to be processed which could not be utilisedfor hydroformylation because of the presence of moieties which wouldpoison and/or inhibit the catalyst or which had a high heavies formingcapability.

It will be understood, that these benefits can be obtained either byoperating the rhodium recovery steps (f) to (i) continuously orperiodically.

The olefin used in the hydroformylation reaction of the presentinvention contains at least one olefinic carbon-carbon double bond.Preferably the olefin contains from 2 to about 20 carbon atoms althoughit will be understood that higher olefins may be used. Included withinthe term “olefin” are not only alpha-olefins, i.e. olefins containingthe group —CH═CH₂ or >C═CH₂ but also internal olefins containing thegroup —CH═CH—, —CR₁═CH—, or —CR₁═CR₁— where R is an organic moiety, aswell as compounds containing both alpha-olefinic and terminal olefinicgroups.

Illustrative olefins include olefinically unsaturated hydrocarbons,e.g., alkenes, arylalkenes, and cycloalkenes, as well as substitutedolefins, e.g. ethers of unsaturated alcohols, and esters of unsaturatedalcohols and/or acids.

Examples of suitable olefins include alpha-olefins (e.g. ethylene,propylene, butene-1, iso-butylene, pentene-1, 2-methylbutene-1,hexene-1, heptene-1, octene-1, 2,4,4-trimethylpentene-1,2-ethylhexene-1, nonene-1, 2-propylhexene-1, decene-1, undecene-1,dodecene-1, octadecene-1, eicosene-1, 3-methylbutene-1,3-methylpentene-1, 3-ethyl-4-methylpentene-1, 3-ethylhexene-1,4,4-dimethylnonene-1, 6-propyldecene-1, 1,5-hexadiene, vinylcyclohexane, allyl cyclohexane, styrene, alpha-methylstyrene,allylbenzene, divinylbenzene, 1,1-diphenylethylene, o-vinyl-p-xylene,p-vinylcumene, m-hexylstyrene, 1-allyl-4-vinylbenzene,beta-vinylnaphthalene, and the like), alpha-alkenols, (e.g. allylalcohol, hex-1-en-4-ol, oct-1-en-4-ol, and the like), alpha-alkenylethers (e.g. vinyl methyl ether, vinyl ethyl ether, allyl ethyl ether,allyl t-butyl ether, allyl phenyl ether, and the like), alpha-alkenylalkanoates (e.g. vinyl acetate, allyl acetate, and the like), alkylalpha-alkenoates (e.g. methyl acrylate, ethyl acrylate, n-propyloct-7-enoate, methyl methacrylate, and the like), alpha-olefinicallyunsaturated aldehydes and acetals (e.g. acrolein, acrolein dimethyl anddiethyl acetals, and the like), alpha-olefinically unsaturated nitriles(e.g. acrylonitrile, and the like), and alpha-olefinically unsaturatedketones (e.g. vinyl ethyl ketone, and the like). The term olefin alsoincludes internal olefins which contain preferably from 4 to about 20carbon atoms. Such compounds have the general formula:R₁R₂C═CR₃R₄in which R₁ and R₂ each represent a hydrogen atom or an organic radicalor together represent a divalent radical which, together with theindicated carbon atoms, form a carbocyclic or heterocyclic ring, and R₃and R₄ each represent an organic radical or together represent adivalent radical which, together with the indicated carbon atoms, form acarbocyclic or heterocyclic ring.

As examples of internal olefins there may be mentioned cis- andtrans-butene-2, 2-methylbutene-2, 2,3-dimethylbutene-2,1,2-diphenylethylene, hexene-2, hexene-3, cis- and trans-heptane-2,decene-2, tetradecene-2, 4-amyldecene-2, 4-methyltridecene-2,octadecene-2, 6,6-dipropyldecene-3, prop-1-enylbenzene,3-benzylheptene-3, cyclobutene, cyclopentene, cyclohexene, cycloheptene,cyclooctene, 1-methylcyclohexene, diethyl maleate, diethyl fumarate,crotonaldehyde, crotonaldehyde dimethyl acetal, ethyl cinnamate, cis-and trans-prop-1-enyl t-butyl ether, and the like.

The hydroformylation reaction may be carried out on a mixture of 2 ormore olefins.

The or each olefin selected for the hydroformylation reaction will becharged to the hydroformylation zone where it will be contacted withhydrogen and carbon monoxide. One or more inert materials, such as inertgases (e.g. nitrogen, argon, carbon dioxide and gaseous hydrocarbons,such as methane, ethane, and propane) may also be present. Such inertgases may be present in the olefin feedstock, the synthesis gas or both.Other inert materials may include hydrogenation by-products of thehydroformylation reaction, for example n-butane where the olefin isbutene-1 or butene-2 and corresponding alkanes for other olefin startingmaterials.

The process may be operated so that apart only of the olefin, e.g. fromabout 15% to about 80% or higher, is converted in passage through thehydroformylation zone. Although the process can be operated on a “oncethrough” basis, with unreacted olefin being exported, possibly for otheruses, after product recovery, it may be desirable to recycle unreactedolefin to the hydroformylation zone.

As some isomerisation of olefin may occur in passage through thehydroformylation zone (for example in the case of butene-1 someisomerisation to butene-2 may occur) when using C₄ olefins or higher,the recycle olefin stream may in such cases contain a minor amount,typically about 10% or less, of isomerised olefin, even though theolefin feedstock is substantially free from other isomeric olefin(s). Inaddition it may contain by-product hydrogenated feedstock. Theconcentration of isomerised olefin(s) and of inert materials in therecycle stream or streams can be controlled in the conventional mannerby talking purge streams at appropriate controlled rates.

The feed of the olefin may be a mixed feedstock containing both internaland alpha-olefin components. For example, it is possible to use a mixedC₄ hydrocarbon feedstock containing, in addition to cis- andtrans-butene-2, also butene-1, iso-butylene, n-butane, iso-butane, andminor amounts of C₁₋₅ alkanes.

The olefin may be subjected to any suitable pretreatment before beingcharged to the hydroformylation zone. However, the ability of theprocess of the present invention to readily remove heavies andregenerate catalyst means that pretreatment to remove impurities and thelike from the hydroformylation zone may not be required or may bereduced.

Thus, for example, in prior art arrangements, the presence of a rhodiumpoison or inhibitor at a level of about 0.5 gram equivalent of rhodiumper cubic meter of feed, will result in complete deactivation in aperiod of the order of 200 days. With the present invention, thispresence in the feed of this level of poisons and/or inhibitors may bereadily accommodated.

The rhodium hydride catalyst used in the process of the presentinvention is preferably a rhodium carbonyl complex comprising rhodium incomplex combination with triphenylphosphine, triphenylphosphite or otherphosphorous ligands for example those described in U.S. Pat. No.4,482,749 which is incorporated herein by reference. Triphenylphosphineis particularly preferred.

The rhodium may be introduced into the reaction zone in any convenientmanner. For example, the rhodium salt of an organic acid, such asrhodium acetate, i.e. [Rh(OCOCH₃)₂.H₂O]₂, can be combined with theligand in the liquid phase and then treated with a mixture of carbonmonoxide and hydrogen, prior to introduction of the olefin.

In one alternative arrangement the catalyst can be prepared from acarbon monoxide complex of rhodium, such as dirhodium octacarbonyl, byheating with the ligand which thereby replaces one or more of the carbonmonoxide molecules. It is also possible to start with the ligand ofchoice and finely divided rhodium metal, or with an oxide of rhodium(e.g. Rh₂O₃ or Rh₂O₃.H₂O) and the ligand, or with a rhodium salt of aninorganic acid, such as rhodium nitrate (i.e. Rh(NO₃)₃.2H₂O) and theligand, and to prepare the active species in situ during the course ofthe hydroformylation reaction.

In another alternative embodiment, it is possible to introduce into thereaction zone, as a catalyst precursor, a rhodium complex such as(pentane-2,4-dionato) dicarbonyl rhodium (I) which is then converted,under the hydroformylation conditions and in the presence of excessligand, to the operative species. Other suitable catalyst precursorsinclude Rh₄(CO)₁₂ and Rh₆(CO)₁₆.

The rhodium complex catalyst is preferably dissolved in the liquidreaction medium which comprises, in addition to the catalytic species,olefin, and a predetermined level of the phosphorous ligand.

Once the plant is operational the reaction medium may also comprise someor all of product aldehyde(s), aldehyde condensation products,isomerised olefin and hydrogenation product(s)derived from the olefin.The inert material detailed above may also be present. The nature of thealdehyde condensation products, and possible mechanisms for theirformation during the course of the hydroformylation reaction, isexplained in more detail in GB-A-1338237, which is incorporated hereinby reference.

Additionally the reaction medium may comprise a solvent, such asbenzene, toluene, acetone, methyl iso-butyl ketone, t-butanol,n-butanol, tetralin, decalin, ethyl benzoate and the like.

Usually, however, it will be preferred to operate in a “natural processsolvent”, i.e. a mixture of olefin or olefins, hydrogenation product(s)thereof, aldehyde product(s) and aldehyde condensation products. Inaddition, solvent from catalyst recovery may be present. However, whenoperating continuously or semi-continuously, it may be preferred to useat start up a solvent, such as acetone, benzene, toluene, or the like,and then gradually to allow this to be displaced by “natural processsolvent” by differential evaporation as the reaction progresses.

The rhodium concentration in the liquid reaction medium may vary fromabout 10 ppm or less up to about 1000 ppm or more, calculated in eachcase as rhodium metal and on a weight/volume basis. Typically therhodium concentration in the liquid reaction medium lies in the range offrom about 40 ppm up to about 200 ppm, calculated as rhodium metal. Foreconomic reasons it will not usually be desirable to exceed about 500ppm rhodium, calculated as metal, in the liquid reaction medium.

In the liquid reaction medium the ligand:Rh molar ratio is 1:1 orgreater but will be limited by solubility constraints.

Make-up ligand may be added and the addition may be continuous orintermittent. It may be added as the essentially pure compound or as asolution in a suitable solvent, e.g. one of the solvents previouslymentioned. If continuous addition is chosen then it can be added insolution form with the aid of a suitable dosing pump.

The hydroformylation conditions utilised in the process of the presentinvention involve use of elevated temperatures e.g. in the range of fromabout 40° C. to about 160° C. or more. Conventionally it will bepreferred to operate at as low a temperature as is possible i.e. fromabout 70° C. to about 95° C. as this will enable a satisfactory reactionrate to be achieved while minimising the risk of heavies formation.

Although the use of higher temperatures has heretofore beendisadvantageous because of catalyst deactivation and/or heaviesformation, the process of the present invention, which allows for readyrecycle and reactivation of the catalyst, means that deactivation and/orheavies formation is not disadvantageous and the higher temperatureswill generally enable improved reaction rates. Thus temperatures in therange of from about 95° C. to about 150° C. or higher may be used.

Thus, for example, in prior art arrangements, an uneconomic system isreached where the hydroformylation of the olefin results in a heaviesconcentration with a recycle stream of greater than 60 wt % within aperiod of 200 days, through either the use of elevated temperaturesand/or presence of involatile material in the feed or formed in thereaction system. In contrast, in the present invention, this level ofheavies may be accommodated.

Elevated pressures are also typically used in the hydroformylation zone.Typically the hydroformylation reaction is conducted at a total pressureof from about 4 bar upwards up to about 75 bar or more. Usually it willbe preferred to operate at a total pressure of not more than about 35bar.

In operating the process of the invention in a continuous manner it isdesirable to supply make up amounts of hydrogen and carbon monoxide inan approximately 1:1 molar ratio, for example about a 1.05:1 molarratio. The formation of such mixtures of hydrogen and carbon monoxidecan be effected by any of the methods known in the art for producingsynthesis gas for hydroformylation, e.g. by partial oxidation of asuitable hydrocarbon feedstock such as natural gas, naptha, fuel oil orcoal.

In operating the process of the invention the total pressure of hydrogenand carbon monoxide in the hydroformylation zone can range from about1.5 bar or less up to about 75 bar or more. The partial pressure ofhydrogen may exceed that of carbon monoxide, or vice versa. For examplethe ratio of the partial pressures of hydrogen and of carbon monoxidemay range from about 10:1 to about 1:10. In general, it will usually bedesirable to operate at a partial pressure of hydrogen of at least about0.05 bar up to about 30 bar and at a partial pressure of carbon monoxideof at least about 0.05 bar up to about 30 bar.

Product recovery can be effected in any convenient manner. In someinstances, for example when using butene-1 or butene-2 as theolefinically unsaturated compound, it is possible to utilise a gasrecycle process similar to that described in GB-A-1582010 which isincorporated herein by reference.

More usually, however, it will be convenient to withdraw a portion ofthe liquid reaction medium from the hydroformylation zone eithercontinuously or intermittently and to distil this in one or more stagesunder normal, reduced or elevated pressure, as appropriate, in aseparate distillation zone in order to recover the aldehyde product(s)and other volatile materials in vaporous form;

the rhodium-containing liquid residue being recycled to thehydroformylation zone either directly or via process steps (f) to (i).

Condensation of the volatile materials and separation thereof, e.g. bydistillation, can be carried out by any conventional means. Aldehydeproduct(s) can be passed on for further purification, whilst a streamcontaining unreacted olefin can be recycled to the hydroformylation zonetogether with any hydrogen and carbon monoxide dissolved in the reactionmedium. A bleed stream can be taken from the recycle stream or streamsin order to control build up of inerts (e.g. N₂) and of hydrogenationproduct(s) in the recycle streams.

When using aldehyde condensation products as solvent, the ratio ofaldehyde to such products in the liquid reaction mixture in thehydroformylation zone may vary within wide limits. Typically this ratiolies in the range of from about 1:5 to about 5:1 by weight.

Under appropriate conditions aldehyde productivities in excess of about0.5 g. mole/liter/hr can be achieved in the process of the invention.Hence it is usually preferred to supply make up olefin to thehydroformylation zone at a rate which corresponds to the aldehydeproductivity of the system under the hydroformylation conditionsselected. As the conversion per pass will usually be less than 100%,typically about 15% to about 80% or higher, it will be necessary toincrease correspondingly the feed rate of the make up olefin if theprocess is to operate on a “once through” basis or to recycle unreactedolefin at an appropriate rate if the process operates with olefinrecycle. Often the aldehyde productivity rate exceeds about 1.0 g.mole/liter/hr, e.g. up to at least about 2 g. moles/liter/hr and therate of supply of make up olefin must then equal or exceed this value.

At least one stream removed from the reactor will be subjected to thecatalyst recovery steps (e) to (i).

The reactor stream may be any stream which is obtained from any point inthe hydroformylation reaction process and which will contain metalhydride catalyst in solution. Thus catalyst may be removed from thereactor, in product stream or in other streams including purge streams.These streams may be treated in accordance with steps (e) to (i) of thepresent invention to recover the catalyst in a form which is suitablefor return to the reactor. The whole of the stream may be subjected tothe steps or the stream may be split and a portion thereof subjected tosteps (e) to (i). The remainder of the stream may be recycled to thereactor.

The reactor stream or a part thereof may be passed directly fortreatment in accordance with steps (e) to (i) or may first undergo anysuitable pretreatment. Where the reactor stream is a product stream, thereaction product may be present during the recovery process of thepresent invention or may be removed at least partially before the streamis contacted with the absorbent.

The various streams from the reactor, following suitable pre-treatment,such as to remove product may be combined for treatment through a singleplant suitable for steps (e) to (i). Alternatively, each stream may betreated separately or streams with similar compositions may be treatedtogether.

The fluid stripping medium of step (g) may comprise hydrogen and aprocess compatible solvent in a single fluid phase, which may be asupercritical phase. In one alternative arrangement the fluid strippingmedium comprises hydrogen and a process compatible solvent in a twophase system. In one arrangement, the process compatible solvent may bea solvent or reactant of the reaction.

Where the fluid stripping medium comprises a liquid phase and a gasphase, the ratio of the gas phase to the liquid phase may be anysuitable value. One suitable example would be one volume of gas to tenvolumes of liquid.

Where the fluid is a single phase, the ratio of dissolved hydrogen tosolvent present may be any suitable value and may be similar to thatused for the two phase system. An important parameter is that anappropriate amount of hydrogen is present.

In one arrangement, the solvent is a liquid which is contacted with agas phase including hydrogen until it is partially or totally saturatedwith dissolved gases. The liquid may then be separated from the gasphase prior to being passed over the metal containing absorbent as asingle phase. The saturated solution may be increased in pressure beforebeing passed over the absorbent as the stripping medium.

Supercritical propane or carbon dioxide may be used as processcompatible solvent. In this arrangement, a supercritical mixtureincluding hydrogen, an optional co-solvent, and ligand may be used asthe stripping fluid.

In a preferred arrangement of the present invention the acidic absorbentis an acidic ion exchange resin. The resin may be a styrenedivinylbenzene copolymer containing sulphonic acid groups or carboxylicacid groups. The resin may have a siloxane-containing backbone and anacidic functional group attached to the backbone. The acidic functionalgroup is preferably selected from the group consisting of aromaticcarboxylic acids, aliphatic carboxylic acids, aromatic sulphonic acidsand aliphatic sulphonic acids, with the sulphonic acids beingparticularly preferred.

Preferably the resin is used in the protonated form. Thus where thesulphonic acid groups are the active groups, they are in the form —SO₃Hand in the presence of phosphines they are at least partially in theform —SO₃ ⁽⁻⁾[HPR₃]⁽⁺⁾. Neutralized sulphonic acid resins, in which someor all of the protons have been exchanged by a cation may also besuitable but are not preferred.

Particularly preferred resins include Amberlyst™ 15 and Amberlyst™DPT-1, with Amberlyst™ DPT-1 being most preferred. Amberlyst™ 15 isavailable from Rohm and Haas (U.K.) Limited of Lennig House, 2 Mason'sAvenue, Croydon CR9 3NB, England and Amberlyst™ DPT-1 ion exchange resinis available from Kvaerner Process Technology Limited of The TechnologyCentre, Princeton Drive, Thornaby, Stockton-on-Tees TS17 6PY, England.

The absorbent may be pre-treated prior to use. The absorbent may bewashed, for example, with methanol to remove water and may also besieved prior to being contacted with the reactor stream.

Without wishing to be bound by any theory, it is believed that theion-exchange resin or other suitable absorbent will allow the absorptionof the metal hydride species onto its surface by a protonation andsubsequent elimination of hydrogen by the following reaction:HRh(X)_(n)+—SO₃H⇄—SO₃Rh(X)_(n)+H₂where each X is a liganding group which may be the same or different andn is an integer of from 2 to 5.

This hydrogen elimination is a reversible reaction and thus the metalspecies remains as a labile species and can be desorbed by the hydrogenin the fluid stripping medium.

Whilst the reactor stream may be contacted with the solid absorbent byany suitable means, the absorbent is preferably a resin bed in a columnthrough which the reactor stream flows. Once the resin bed has beenloaded with the metal, the stripping medium is then preferably passedthrough the resin bed and into the reactor. In one alternativearrangement, the reactor stream may be contacted with the absorbent in astirred vessel. In this arrangement, the contact will be a repeatedbatch process.

The contact of the reactor stream with the solid acid absorbed resin maybe carried out at any suitable temperature. Temperatures of from 0° C.to about 120° C. may be used with those of from about 20° C. to about100° C. being preferred. A temperature in the region of from about 50°C. to about 95° C. is particularly preferred as the higher temperaturewill facilitate the removal of the metal from solution and its loadingonto the absorbent. The temperatures and pressures will generally beselected such that any solids formation such as crystallisation ofligand or ligand oxide is avoided.

As the catalyst is absorbed onto the resin, a catalyst depleted solutionwill remain and may be removed from the system. The further treatment ofthis solution will depend on the content of the stream. Where thereaction stream treated in accordance with the present invention is astream containing heavies, the catalyst depleted solution willpreferably be removed. The catalyst depleted solution may be passedthrough a conventional catalyst collection system to trap the inactivecatalytic metal and any trace amounts of the catalyst remaining.

The stream to be treated may be concentrated before being contacted withthe acidic absorbent. The concentration will preferably occur by removalof volatilisable material. The reactor stream or the concentrated streammay require dilution with a solvent compatible with the absorbent beforeit is contacted with the absorbent. Any suitable solvent may be used.Normally, the solvent will be miscible with the reactor stream orconcentrated stream. Suitable solvents include xylene and toluene.

Where the stream to be treated includes inactive catalyst this may beexposed to the absorbent but may not react therewith and if no reactionoccurs will be removed with the non-volatile components.

However, where the inactive catalyst has been deactivated by theformation of clusters, these may be broken before the stream iscontacted with the absorbent such that they can be absorbed by theabsorbent and treated with the stripping medium. By this means thisinactive catalyst may be regenerated such that it may be returned to thereactor and take part in the reaction.

Thus according to a preferred aspect of the present invention, thestream is preferably passed through an oxidiser where air is passedthrough the solution to break down the clusters before being broughtinto contact with the absorbent. For a rhodium catalyst havingtriphenylphosphine as a ligand, the air will break down the rhodiumclusters by oxidation of the phosphido bridges.

The oxidiser may also at least partially oxidise any trivalentphosphorous compounds which may be present to the pentavalent form (i.e.conversion from phosphites to phosphates).

Where the oxidiser is present, the oxidation step, in addition tobreaking up the clusters, may additionally change the oxidation state ofthe metal in that it will be converted to a simple cationic form. ThusRh²⁺ and Rh³⁺ will be formed.

Additionally or alternatively, the reaction stream may be treated inaccordance with one or more of the organic reagents described in U.S.Pat. No. 4,929,767 and U.S. Pat. No. 5,237,106 which are incorporatedherein by reference.

To improve the absorbability of the rhodium onto the absorbent, theprocess may additionally include, treating the catalyst such that it isin a suitable state for absorption. The catalyst preferably is subjectedto hydrocarbonylation where it is treated with an organophosphorousligand such as triphenylphosphine, carbon monoxide and hydrogen toreform the catalyst in the form Hrh(CO)(PPh₃)₃.

Once the rhodium has been loaded onto the absorbent, the absorbent maybe washed to further remove impurities. In addition to removingimpurities by means of their not being absorbed by the absorbent suchthat they are removed in the catalyst depleted reactor stream or by thewashing described above, the absorbent may also serve to remove someimpurities. For example, iron, nickel and/or chromium may be present.These will generally also be absorbed by the absorbent but will not beretrieved by the stripping medium of the present invention. Thus thestream recycled to the reactor will be free of these impurities.

Whatever pre-treatments of the stream are carried out, and whateverwashing is carried out, if any, the partial pressure of the gaseousphase of the stripping media, or of the hydrogen component of thesupercritical phase or the fluid phase, for removing the absorbed metalmay be of any suitable value. Partial pressures of about 200 kPa orhigher may be particularly advantageous. The upper limit on the partialpressure will be dictated by the equipment rating.

The stripping media fluid preferably additionally includes carbonmonoxide. The presence of carbon monoxide has been found to offerimproved results and is particularly appropriate as the catalyst complexincludes CO as a ligand.

The fluid of the stripping media preferably includes a liquid phasewhich comprises liquids which are compatible with the reactants, othercompounds and products in the hydroformylation zone, such that theproduct stream containing the rhodium catalyst may be returned to thereactor without further processing. The fluid is preferably alsocompatible with product recovery operations.

In one embodiment of the present invention, the fluid of the strippingmedia will comprise liquids which are required to be present in thehydroformylation zone such as ligands and raw materials. Thus, where thecatalyst is HRh(CO)(PPh₃)₃ in one arrangement, the liquid phase willcomprise triphenylphosphine. Additionally or alternatively, the liquidphase may comprise olefin and/or triphenylphosphine. Thus, a preferredprocess of the present invention allows that no additional substancesare fed to the hydroformylation zone other than those required for orproduced in the hydroformylation reaction.

In one alternative embodiment, the fluid includes material that is usedin the catalyst recovery process but which is inert to thehydroformylation process. The material is preferably recoverable andrecyclable from the hydroformylation zone to the rhodium recoverysection of the plant. One example of suitable material is toluene whichmay be used as a solvent or diluent in the rhodium recovery process.

Whilst the reactor stream may be contacted with the solid absorbent byany suitable means, the absorbent is preferably a resin bed in a columnthrough which the stream collected in step (e) flows. Once the resin bedhas been loaded with the rhodium, the stripping medium is thenpreferably passed through the resin bed and into the reactor.

The stripping process will preferably simultaneously regenerate theabsorbent bed for further subsequent absorption of rhodium from a freshstream. However, it may be advisable to wash the resin at leastperiodically to remove any impurities, ligand and the like which maybuild up over several passes of the reactor stream.

The stripping may be carried out at similar temperatures to those usedfor the loading. However, lower temperatures favour the rhodium beingdesorbed and going into solution. Suitable temperatures include fromabout 20° C. to about 70° C. This is particularly the case where higherpartial pressures of hydrogen are used.

To allow for continuous treatment of catalyst from the reactor, theplant may include at least two beds of absorbent operated in parallel.The reactor stream will be passed through a first bed of absorbent suchthat the rhodium is substantially removed from the stream. Once the bedhas been loaded, the stream will be switched to flow through the secondbed. Whilst the second bed is being similarly loaded, the strippingmedium will be applied to the first bed such that the rhodium isdesorbed. The procedure will then be reversed such that the first bed isbeing loaded while the second bed is being desorbed. Thus in a preferredarrangement, the process is effectively continuous.

Thus the present invention provides a process the plant for which iscost-effective to construct and to operate and which enables thecatalyst to be recovered from reactor streams and returned to thereactor.

A further advantage of the present invention is that where reactants,ligands and the like are used for the stripping medium and these arepassed via the absorbent where stripping occurs, to the reactor, notonly are no additional substances, or only inert substances, introducedinto the reactor, there are no costs associated with the strippingmedium.

The recovery of the catalyst in accordance with the present inventionmay also enable poisoned and/or inhibited catalyst to be reactivated.Without wishing to be bound by any theory, it is believed that the metalis attracted to the absorbent and the poison/inhibitor is removed in thecatalyst depleted stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example withreference to the accompanying drawings in which:

FIG. 1 is a schematic diagram embodying the process in accordance withthe present invention;

FIG. 2 is a schematic diagram embodying steps (e) to (i) of the presentinvention;

FIG. 3 is a graph of aldehyde, heavies and olefin content against timefor Comparative Example 1;

FIG. 4 is a graph of aldehyde, heavies and olefin content against timefor Example 1;

FIG. 5 is a graph of aldehyde, heavies and olefin content against timefor Comparative Example 2;

FIG. 6 is a graph of aldehyde, heavies and olefin content against timefor Example 2;

FIG. 7 is a graph of aldehyde, heavies and olefin content against timefor Comparative Example 3; and

FIG. 8 is a graph of aldehyde, heavies and olefin content against timefor Example 3.

DETAILED DESCRIPTION OF THE DRAWINGS

It will be understood by those skilled in the art that the drawings arediagrammatic and that further items of equipment such as feedstockdrums, pumps, vacuum pumps, compressors, gas recycling compressors,temperature sensors, pressure sensors, pressure relief valves, controlvalves, flow controllers, level controllers, holding tanks, storagetanks and the like may be required in a commercial plant. Provision ofsuch ancillary equipment forms no part of the present invention and isin accordance with conventional chemical engineering practice.

As illustrated in FIG. 1, a liquid comprising olefin is fed to theapparatus in, line 1 where it is joined by a catalyst solution in line2. The mixed liquids continue in line 3 to the reactor 4. The reactor isfitted with an agitator 5 which is capable of inducing the gas from thereactor head space into the liquid and anti liquid vortex baffles (notshown). The reactor is also equipped with an internal cooling coil 6arranged such that a controlled flow of a fluid enables the reactor tobe maintained at the desired temperature. Generally an externalelectrical heater (not shown) is used for the start-up of the equipment.

The reactor 4 is supplied with a 1:1 molar ratio mixture of carbonmonoxide and hydrogen in line 7. A trim stream of carbon monoxide and/orhydrogen is supplied in line 8 so that the ratio of the gas partialpressures in the reactor head space can be adjusted to any desiredvalue. The gas stream 9 is sparged into the base of the reactor. Theunreacted gases pass out of reactor 4 by line 11. This stream passes todemister vessel 12 where any catalyst containing liquid droplets arecollected to return to reactor 4 by line 13.

The gases continue by line 14 to condenser 15 supplied with a coolantfluid in line 16. The resulting condensate passes via line 17 to productrecovery and the uncondensed gases pass from the system in line 18.

The liquid leaves the hydroformylation reactor 4 and passes to theproduct recovery equipment by line 10. Level control devices (not shown)ensure that a constant liquid inventory is maintained in the reactor.

The liquid in line 10 comprising of catalyst components,hydroformylation products, unreacted olefin feed, hydrogenated,isomerised and unreacted olefin, as well as aldehyde condensationproducts with some dissolved gases passes into vaporiser 19 suppliedwith a heating fluid in line 20.

The mixture of liquid and vapour passes via line 21 into vapour/liquidseparation vessel 22. Vessel 22 is equipped with droplet agglomerationdevice 23 which is irrigated by a small stream of product from line 58to wash any ligand and rhodium values back into the base of vessel 22.

The vapour leaves by line 24 and the liquid leaves by line 25. Theliquid in line 25 which is now free of vapour and which comprisescatalyst is pumped by catalyst recycle pump 26 into line 27. A majorportion of the catalyst solution is recycled in line 28 via line 2 tothe reactor 4. It will generally be mixed with any fresh feed from line1 prior to its addition to reactor 4.

A minor portion of the stream in line 27 is passed in line 29 to therhodium recovery unit. Stream 73 will generally comprise recovered andmake up rhodium, recovered and/or make up triphenylphosphine (or otherligand) as well as solvents and hydroformylation reaction by-products.

The vaporisation conditions of temperature and pressure are adjustedsuch that the liquid level in vessel 22 is constant and this sets thetotal liquid inventory of the reaction system.

The vapours in line 24 pass to condenser 30 which is supplied withcoolant in line 31. The cooled mixture then leaves by line 32 and joinsthe liquid from line 17 in product vessel 33. The liquid passes fromvessel 33 via line 34 to distillation column 35. The vapour from vessel33 passes through line 36 to compressor 37 and then in line 38 todistillation column 35. The compressor 37 and its associated controlequipment (not shown) determines the pressure in vessels 22 and 33 andhence the product vaporisation temperature in vaporiser 19.

In column 35, which is illustrated with distillation trays, the aldehydeproducts are recovered as bottom products in lines 39 and 40. Somealdehyde product recirculates through lines 41, 42 and 45 via reboiler43 provided with a heating fluid in line 44. The heating fluid providesthe energy supply for the distillation.

The overhead vapours from column 35 are partially condensed in refluxcondenser 46 provided with cooling coil 47.

The uncondensed vapours pass on in line 48 through-compressor 49, line50 and condenser 51 with cooling coil 52. This arrangement determinesthe pressure in the distillation system as well as providing a higherpressure in the condenser 51.

The liquid and gas pass by line 53 to separator 54. The gases leave thesystem by line 55. The liquid is partially returned as reflux to theupper part of column 35 by line 56 and the nett make of liquid isrecovered in line 57. This liquid can comprise any volatile solventsadded as part of stream 73 which is added into line 28 as well ascomprising unreacted and isomerised olefin and paraffin or othervolatile components of the olefin feed stream 1. This stream (afteroptional further processing) can for example be used in the rhodiumrecovery and recycle section of the equipment.

In use, the equipment is brought into operation by flushing all oxygenfrom the system with nitrogen or argon. Then by filling the reactor 4and vessel 22 with a liquid such as toluene (or pure aldehyde ifavailable) containing dissolved ligand such as triphenylphosphine and arhodium catalyst precursor complex (such as rhodium dicarbonylacetylacetonate). A liquid recirculation through the reactor 4, vessel22 and lines 25, 28, 2 & 3 is established by pump 26.

Olefin feed is supplied at a low rate to the system via line 1 andcarbon monoxide plus hydrogen by line 7. The reactors are warmed towardsoperating temperature and the liquid inventory in the system maintainedby vaporising liquid in vaporiser 19 as required.

When the reaction starts, which can be noted on instrumentation as gasuptake, the product aldehyde accumulates in the system and the start-upsolvent preferentially leaves. The distillation equipment iscommissioned and solvent progressively leaves the system.

Eventually aldehyde starts to accumulate in the base of column 35.Pressures and temperatures are adjusted until normal operatingconditions are attained and aldehyde product leaves in line 40. Whenheavies start to accumulate in the catalyst recycle solution which canbe determined by analysis of the composition of line 27, a stream ofmaterial is taken from line 29, treated as described below and recoveredand with make-up material returned in line 73.

Stream 29 is then passed to the rhodium recovery zone which isillustrated in FIG. 2. This stream 29 will first be passed to anevaporator 74, such as a wiped film evaporator, to separate anyremaining volatile components. Volatile components of the stream will beremoved in line 75 and may be subjected to further treatment includingcondensation and separation. Triphenylphosphine may also be removed inline 75.

The residue of unvaporized portions which will now be a concentratedstream is passed in line 76 to oxidiser 77 where air is bubbled throughthe liquid. The air is introduced in line 78 and is purged in line 79.The air will serve to break any cluster rhodium molecules so that thispreviously inactive rhodium can be absorbed by the ion exchange resin.

The stream including the rhodium leaves the oxidiser in line 80 and isthen pumped, by pump 82, to a hydrocarbonylation zone 81. In thisstirred tank vessel, the catalyst containing stream is mixed withtriphenylphosphine added in line 83 and is contacted with hydrogen andcarbon monoxide which is added in line 84. The triphenylphosphine addedvia line 83 may be recycled triphenylphosphine recovered from line 75.

The carbonylated catalyst is then removed in line 85 and is passed intothe first absorber column 86′ which is packed with ion-exchange resinAmberlyst™ DPT-1. The resin bed will be at a temperature in the regionof about 75° C. to aid the rate of absorption of the rhodium by theion-exchange resin.

As the stream passes through the absorbent bed, the rhodium is absorbedonto the resin and the non-volatile heavies and impurities are removedin stream 87′ for optional further processing. Due to the value of therhodium, the stream may be passed through a conventional rhodiumrecovery system (not shown) to collect any catalyst which may passthrough the resin bed, which may be inactive catalyst, for off-siteregeneration.

Once column 86′ has been loaded, the stream from vessel 81 will bedirected to column 86″ so that the removal of the rhodium can be carriedout as a continuous process. When the resin is loaded in column 86″, thecatalyst depleted stream is removed in stream 87″.

The rhodium loaded in column 86′ is then stripped from the resin using astripping medium which is passed through the column. Where the strippingmedium contains a mixture of organic liquids, these will be combined inmixer 88. The liquid phase is preferably a combination of processcompatible solvents and/or olefin added in line 89 andtriphenylphosphine added in line 90.

The olefin may be fresh olefin which will be passed through the resinbed before being added to the reactor. Alternatively, the olefin may berecycled olefin, isomerised olefin and paraffin recovered from streamsremoved from the hydroformylation reaction zone.

Similarly, the process compatible solvents may be fresh solvents orrecycled solvents recovered from streams removed from thehydroformylation reaction zone or the downstream product recoverysystems.

The triphenylphosphine may be fresh triphenylphosphine or it may berecycled, for example from stream 75 of volatile compounds removed fromthe wiped film evaporator 74.

This combined liquid phase for the stripping medium is removed from themixer 88 in line 91 where it is combined with hydrogen and carbonmonoxide of the gaseous phase which is added in line 92. The strippingmedium will be passed through column 86′ which is held at ambient orhigher temperature.

The resulting stream, which will contain rhodium, hydrogen, carbonmonoxide, triphenylphosphine and olefin and/or process compatiblesolvents is then returned to the reactor in line 73.

The removal of the rhodium allows resin bed 86′ to be used to absorbfurther rhodium. Resin bed 86″ can then be stripped by repeating theprocess described above. Thus the process can be operated in acontinuous manner.

Whilst the present invention has been illustrated with one reactor,vaporiser, etc., it will be understood that where appropriate thenumbers of some or all of these could be increased.

The invention is illustrated further in the following Examples.

COMPARATIVE EXAMPLE 1

Hydroformylation is carried out on 1-decene in a hydroformylation plantas described above is run with a rhodium concentration in the reactor of220 ppm, a triphenylphosphine concentration of 10 wt %, hydrogen andcarbon monoxide partial pressures each at 30 psi and at a reactortemperature of 110° C. such that non-volatile components gradually buildup in the recycle loop. No material is taken in line 29 for catalystrecycle and the system is run until the shut down criterion of excessheavies in the catalyst recycle solution is reached. The design of theplant apparatus imposes a maximum content of heavies material in therecycle. For the purposes of these examples, the maximum heavies contentis taken to be 60 wt %. When this point is reached, the run must beterminated as operation is no longer feasible.

FIG. 3 illustrates the performance of the reactor where no recycling ofthe rhodium is used and illustrates the decline of olefin conversion inthe reactors and the build up of heavies. In this comparative examplethe heavies concentration exceeds 60 wt % at approximately 350 hours.

EXAMPLE 1

The reactor is again run at 110° C. but a purge equivalent to 0.2 wt %of the recycle flow is taken and treated to rhodium recovery asdescribed in FIG. 2 and returned to the reactor.

FIG. 4 illustrates how the conversion of olefin and overall performanceof the reactor reaches a steady state after approximately 1000 hourson-line with the heavies being controlled well below 60 wt % allowingthe reactor to be run continuously at these conditions.

COMPARATIVE EXAMPLE 2

Example 1 is repeated with the reactors running at a temperature of 110°C. and purge rate of 0.2% of the recycle flow. The reactor is startedwith a rhodium concentration of 500 ppm. The feed also contains a poisonsuch that 1 liter of feed contains sufficient poison to react withapproximately 1 mg of rhodium. The purge from the recycle stream istreated to recover the rhodium but the poison is not separated from therhodium such that it is recycled to the reactor. As a consequence theheavies reaches a steady state level after 500 hours but the activitydeclines as the rhodium is deactivated. The productivity falls offdramatically at around 2500 hours as illustrated in FIG. 5.

EXAMPLE 2

Comparative Example 2 is repeated except that the poison in the purge isnot reintroduced with the recovered rhodium. After 1000 hours theheavies concentration has reached steady state at approximately 50 wt %.The olefin conversion levels out but continues a small decline for afurther 5000 hours. After 5000 hours steady state is achieved asillustrated in FIG. 6

COMPARATIVE EXAMPLE 3

Comparative Example 1 is repeated, however in addition to heaviesforming as a result of aldol condensation reactions, the feed contains0.1 wt % involatile material. As a result the level of heavies in therecycle increases more rapidly than shown in Comparative Example 1. Inthis example the maximum allowable heavies concentration is exceededafter only 200 hours as illustrated in FIG. 7.

EXAMPLE 3

Example 1 is repeated with a feed containing 0.1 wt % involatilematerial and an increased purge rate of 0.4 wt %. As illustrated in FIG.8 the heavies in the recycle reaches a stable maximum of approximately50 wt % after 1000 hours.

EXAMPLE 4

A solution of hexene (50 ml) in texanol (50 ml) was hydroformylated toextinction using a catalyst prepared from 0.1 mmol of Rhodium(acac)(CO)2and 0.6 mmol of a bidentate phosphite of the formula(ArO)2P(OAr—ArO)P(OAr)2 where Ar represents various aryl functionalgroups. Amberlyst DPT-1 was then added to the autoclave (8 g, dryweight). After stirring at 65° C. for 1 hour the concentration ofrhodium in solution had dropped to 25 ppm. The autoclave was thenpressurised to 1000 psig with hydrogen and cooled to room temperature.After 18 hours the concentration of rhodium in solution had increased to75 ppm.

1. A continuous hydroformylation process for the production of analdehyde by hydroformylation of an olefin which comprises: (a) providinga hydroformylation zone containing a charge of a liquid reaction mediumhaving dissolved therein a rhodium hydroformylation catalyst comprisingrhodium in combination with carbon monoxide and a ligand; (b) supplyingthe olefin to the hydroformylation zone; (c) maintaining temperature andpressure conditions in the hydroformylation zone conducive tohydroformylation of the olefin; (d) recovering from the liquidhydroformylation medium a hydroformylation product comprising aldehyde;(e) recovering from the hydroformylation zone a stream comprising therhodium catalyst; (f) contacting at least a portion of the stream with asolid acidic absorbent under process conditions which allow at leastsome of the rhodium to become bound to the absorbent; (g) subjecting therhodium bound to the absorbent, under process conditions which allowdesorption of the metal, to a fluid stripping medium comprising hydrogenand solvent; (h) recovering the rhodium hydride catalyst; and (i)recycling the rhodium hydride catalyst to the hydroformylation zone. 2.A process according to claim 1 wherein the stream from step (e) isdivided and a first part is recycled to the hydroformylation zone and asecond part is subjected to steps (f) to (i).
 3. A process according toclaim 2 wherein the second part is at least about 0.01% of the streamfrom step (e).
 4. A process according to claim 1 wherein the olefin isone of more olefin selected from C₂ to C₂₀ olefins.
 5. A processaccording to claim 1 wherein the olefin is not subjected to pretreatmentbefore being charged to the hydroformylation zone.
 6. A processaccording to claim 1 wherein the rhodium hydride catalyst is a rhodiumcarbonyl complex comprising rhodium in complex combination withtriphenylphosphine.
 7. A process according to claim 1 wherein thehydroformylation zone is operated at a temperature which will causethermal deactivation of the catalyst.
 8. A process according to claim 1wherein the hydroformylation zone is operated at a temperature of fromabout 40° C. to about 180° C.
 9. A process according to claim 1 whereinthe feed to the hydroformylation zone includes poisons, inhibitors orpoisons and inhibitors.
 10. A process according to claim 9 wherein thehydroformylation zone includes at least 0.5 gram equivalent of rhodiumof poisons, inhibitors or poisons and inhibitors per cubic meter offeed.
 11. A process according to claim 1 wherein the feed to thehydroformylation zone includes heavies or compounds likely to formheavies in the hydroformylation zone or both.
 12. A process according toclaim 1 wherein the fluid stripping medium is a single fluid phase. 13.A process according to claim 12 wherein the single fluid phase is asupercritical phase.
 14. A process according to claim 12 wherein thefluid stripping medium comprises two fluid phases.
 15. A processaccording to claim 1 wherein the stream collected in step (e) containsnon-volatile by-products of the reaction.
 16. A process according toclaim 1 wherein the stream having been contacted with the solid acidicabsorbent is removed.
 17. A process according to claim 1 wherein theacidic absorbent is an ion-exchange resin.
 18. A process according toclaim 1 wherein the acidic absorbent is a styrene divinyl copolymercontaining sulphonic acid groups or carboxylic acid groups.
 19. Aprocess according to claim 1 wherein the acidic absorbent has asilica-containing backbone and an acidic functional group attached tothe silica.
 20. A process according to claim 19 wherein the acidicfunctional group is an aromatic carboxylic acid, an aliphatic carboxylicacid, an aromatic sulphonic acid or an aliphatic sulphonic acid.
 21. Aprocess according to claim 1 wherein step (g) is carried out at atemperature of from about 20° C. to about 100° C.
 22. A processaccording to claim 21 wherein the temperature is in the region of about50° C. to about 95° C.
 23. A process according to claim 1 wherein thestream recovered in step (e) is concentrated prior to contact with theacidic absorbent.
 24. A process according to claim 1 wherein the streamrecovered in step (e) is diluted with a solvent compatible with theabsorbent before it is contacted with the absorbent.
 25. A processaccording to claim 1 wherein the stream recovered in step (e) issubjected to oxidation to break clustered catalyst prior to beingcontacted with the acidic absorbent.
 26. A process according to claim 25wherein the stream having been subjected to oxidation is treated tohydrocarbonylation.
 27. A process according to claim 1 wherein thegaseous phase of the stripping medium additionally includes carbonmonoxide.